The present invention relates to a mounted camera used in conjunction with and an illumination source, and possibly a field lens, to provide a compact inspection system which is extremely small in size and facilitates use within the small confines of semiconductor, processing equipment.
There are a variety of known illumination sources for illuminating a flat surface to be inspected such as a laser-etched art work semiconductor lead framework. However, most of the known systems are of a relatively large size which do not easily fit within the confines of currently available semiconductor processing equipment.
In particular, known arrangements typically affix a ring of LEDs to the underside of rather large and bulky inspection equipment. The ring of LEDs is centered about the optical axis which extends normal to the inspection surface. This illumination geometry is useful for imaging xe2x80x9cmirror meltingxe2x80x9d by a laser of desired art work on a diffusely reflecting metal surface. In the area affected by the laser, the diffused surface finish is melted to convert that surface area into a highly specular surface finish. This specular surface finish reflects the low-angle dark field illumination off at an equivalent low-angle causing it to appear dark in the field of view. The diffuse background finish reflects some of the incident low-angle illumination along the optical axis into the camera lens and hence that area appears bright. This combination causes the xe2x80x9cmirror meltingxe2x80x9d laser mark to appear in high contrast, e.g. black on a white surface, rendering it fairly easy to decipher by conventional machine vision systems.
If the lead frame surface finish is highly specular, however, the dark field illumination geometry described above will cause the surface to appear black, hence rendering invisible any xe2x80x9cmirror meltingxe2x80x9d art work, e.g. a dark field on a dark field. For laser etching to be visible under a dark field illumination, on such highly specular surface, the surface must be optically xe2x80x9croughed upxe2x80x9d by the laser. For example, the surface must be etched so as to form small craters or pits. Under darkfield illumination, only the rim of the laser pits will reflect light to the camera while the valleys of the pits will reflect the light to the surrounding environment. If the pits are small enough and spaced closely enough together they can be made to appear as a xe2x80x9csolidxe2x80x9d feature. If the pits are isolated and enlarged, however, they appear as bright rings on a dark background, potentially causing problems with the inspection algorithms currently used in prior art systems.
Wherefore, it is an object of the present invention to overcome the aforementioned problems and drawbacks associated with the prior art designs.
In one embodiment, the present invention relates to a design which provides a bright field illumination via a curved beam splitter which is positioned between the camera lens and a penta-prism. In applications where the mark being imaged is relatively small, the bright field source does not have to be significantly larger in size than the camera aperture itself.
The invention relates to a miniature inspection system for observing an object, the inspection system comprising: a camera for inspecting an object when located at an inspection location, and an optical axis being defined between the camera and the object when located at the object inspection location; a ring light being located concentrically with respect to and along the optical axis, at a location between an entrance aperture of the camera and the object, when located at the object observing location; and a field lens being located along the optical axis at a location between the camera and the object, when placed at the object observing location.
The present invention also relates to a miniature inspection system for observing an object, the inspection system comprising: a camera for inspecting an object when located at an inspection location, and an optical axis being defined between the camera and the object when located at the object inspection location; a ring light being concentrically disposed with respect to and along the optical axis at a location between an entrance aperture of the camera and the object, when located at the object observing location; and a penta-prism being located along the optical axis such that light reflected from the object, along the optical axis, is reflected by the penta-prism along the optical axis toward the entrance aperture of the camera.
Also, the present invention relates to a miniature inspection system for observing an object, the inspection system comprising: a camera for inspecting an object when located at an inspection location, and an optical axis being defined between the camera and the object when located at the object inspection location; a ring light being concentrically disposed with respect to and along the optical axis at a location between an entrance aperture of the camera and the object, when located at the object observing location; and a fresnel lens being located between the ring light and the object, when placed at the object inspection location, for altering the light supplied to the object when placed at the object inspection location.
The term xe2x80x9cdiffusexe2x80x9d, as used in this specification and the appended claims, means a light source which is dispersed over a broad range of incident angle of azimuth and elevation with respect to the object being observed, and the light source approaches complete coverage over the area where the light is directed, i.e. greater than 25% of the possible angular range of incident light. The term xe2x80x9cconcealedxe2x80x9d, as used in this specification and appended claims, when referring to the diffuser and the object to be inspected, means that the surface emitting the diffused light from the diffuser is positioned such that the emitting surface of the diffuser can not directly illuminate the object, i.e. only indirect illumination of the object by reflection of light off the beam splitter or the side wall (s) of the housing or supplying light through the beam splitter can occur.